When producing cellulose-based products, a roll press is frequently used for washing and dewatering the cellulose-based pulp. The pulp is passed between two cooperating press rolls installed in the roll press, the press rolls having a perforated outer surface, a so called mantle surface, whereby the outer surface is permeable to liquid pressed out of the pulp, and the pulp is pressed in the roll nip, or the press nip, between the press rolls, whereby liquid is pressed out of the pulp. The roll press also includes one or more washing zones prior to the press nip. One example of such a roll press is disclosed in European Patent No. 1,035,250, in which the central axes of the press rolls lie in substantially the same horizontal plane, and the pulp is fed in the direction of rotation of the press rolls through the press nip, and the pulp passes through the press nip between the press rolls from below upwards.
U.S. Pat. No. 3,730,079 discloses a press comprising two press rolls rotatable about parallel axes, wherein one of the press rolls is laterally movable relative to the other to vary the cross-section of the press nip therebetween. A pressing force is applied to the laterally movable press roll by a plurality of separate link systems actuated by individual fluid pressure operated actuators. Pneumatically expansible tubes or springs are provided to urge the movable press roll away from the other press roll. The object of this press is to maintain the axes of the press rolls parallel while permitting relative lateral movement of the press rolls.
However, there is a need for improved processing of pulp in an apparatus for washing and dewatering pulp comprising two rotatable press rolls, which can more accurately provide pulp with the desired quality, and which increases the capacity of the apparatus.
One object of the present invention is thus to provide for improved processing of pulp in an apparatus for washing and dewatering pulp comprising two rotatable press rolls.